Electric power megaphone system



Marsh i943.

R, slLiERMAN ELECTRIC POWER MEGAPHONE SYSTEM Filed Ooi. 4, 1941 ITI-.III

a ""II i 1NVENTORt y Patented Mar. 16, 1943l UNITED STATES PATENT OFFICE vELETRIC POWER MEGAPHGNE SYSTEM Ralph Silverman, Pittsburgh, Pa. Application October 4, 1941, Serial No. 413,620

z claims. (ci. 179-1) This invention relates to loud-speaker systems, and particularly to a loud-speaker system m-ade up to provide a simple, and easily operable, electric power megaphone,

One object of my invention is to provide a simple, portable loud-speaker system, including a combination microphone and loud-speaker unit,

' lthat may be utilized and employed as an electric power megaphone, to throw the human voice over a substantial distance with directional control.

Another object of my invention is to provide an amplifying system with an electric power megaphone that will provi-de simple directional control and instantaneous repsonse for intermittent operation, as, for example, for use by -a drilling `instructor on a drilling ground of large area, or

for similar usage, where-directional control is` desired with carrying distance.

Another object of my invention is to provide an electric power megaphone in which an electro-dynamic s'peaker unit is employed, and a mi- 'Another object of my invention is to provide an electric power meg-aphone system including a megaphone'of the foregoing type or'construction,

" with a portable unit 'to serve as an amplifying circuit between the microphone and the electro-magnet of the dynamic speaker unit with the ampliiication constants adjusted toa fixed-level below the amplification level that would cause feed back oscillation.

Another object of my invention is to provide an electric power megaphone as a complete arti-j cle of manufacture, in which the dynamic speaker unit is provided-with a reiiex type exponential horn, having the back of the horn completely closed, and employed to serve as a mounting for the microphone, with an operating handle, at the base or side wall of the horn, to'serve as a support and manipulator for the horn, with an of which the operator may connect the amplifying equipment into a circuit between the microphone and the horn, when the megaphcne is` to be put into use.

Another object of my invention is toprovlde an electric power megaphone system of the'fiire-` going type, in which the amplifying equipment is electric control switch in the handle, by means so set up between the microphone and the electromagnet of the electro-dynamic speaker, that a substantially instantaneous response may be established with no perceptible delay. or lag in obtaining the top operation level of the equipment at the closure of the control switch in the handle.

Another object of my invention is to provide an electric power megaphone system of the foregoing character, with provision for a remote auxiliary control microphone to operate the megaphone, as, for example, by a second person spaced a distance away from the person handling the megaphone itself.

The manner in which my invention is applied is illustrated in the accompanying drawing in which- Figure 1 is a schematic view and circuit diagram of a combination soundfreproducer or loudspeaker device, with a microphone structurally applied to constitute the unit a power megaphone, with a plug connector to connect an amplifying circuit between the microphone and the. loudspeaker;

Figure 2 is a diagram of the circuit connections from the microphone and the speaker coil to the handle switch and the terminals of the plug con-t nector;

Figure 3 is a diagram illustrating the arrangement of the various elements of the equipment to show how the batteries and the amplifying equipment are disposed in one small portable box to be carried, for example, on a shoulder strap by the operator, with a single cable plug connection from that battery and ampliiler box to the combination megaphone unit; and with an auxiliary plug connection for an auxiliary microphone unit; and

Figure is a diagram of the circuit oi an auxiliary plug for connecting an auxiliary microphone to the amplifying circuit. l

As shown in the drawing, the electric power megaphone Il) comprises a microphone II mount` ed on the back of an electric sound-reproducer or loud-speaker I2. The megaphone, as a unit, is adapted to be mechanically controlled and directed by a supporting handle I3. The energiza` ltion of the megaphone is controlled by a trigger switch I4 mounted in the handle I3. Operation of the switch I4 connects the microphone II and the speaker I2 through a two-stageaudio frequency amplifier, comprising a first stage amplifler tube I5 and a second stage or output amplifier tube I6.

Energy for the amplifying system is derived from a set of A batteries Il and a set of B batteries I8. The A batteries I1 supply energy to the microphone circuit and to the filaments of the two tubes I and IB. That energizing circuit from the A battery is controlled by the trigger switch Ill mounted on the handle for manipulating the power megaphone as a unit.

In order to permit the megaphone to be easily connected to, and disconnected from, the amplifying equipment, a plug and socket connection is provided, consisting of a plug 2e and a socket 2 I. The plug 28 is provided with terminals a, b, c, and d connected to the switch, the microphone and the speaker coil, as shown. The socket 2l is provided with similarly placed terminals connected to the A battery and circuit terminals as shown in Figure 3.

To permit the use of the megaphone system by-a second person, independently of the first person, when the system is set up, a second plug and socket connection is provided, including an auxiliary plug 22 and a socket 23, each with terminals connected as shown in Figure 4.

In order to permit the megaphone unit to be handled and operated as a simple horn, with universal freedom of directional control, the microphone unit II is mounted directly on the rear of the shell of the sound-reproducer I2.

The reproducer I2. shown in the drawing, comprises a permanent magnet or motor unit 25 and a diaphragm (not shown) that supports a coil which will cause movement of the diaphragm according to electro-magnetic reaction of the coil flux and the magnet fiux. The magnet and dia.- phragm are mounted at the small end of an exponential horn 26, shown as a reflex type exponential horn that serves as its own enclosing and protecting shell for the operating electromagnet. The front end 21, of the horn, is open, and the rear end of the horn is completely closed, particularly by a conical element 28 that helps to maintain the proper internal space dimensions for the exponential function.

The electro-magnet 25, and a portion of the horn, constituting the small end of the horn, are supported as a unit on the outer shell 26 of the horn, by means of three mounting bolts 29, with suitable spacing devices 30. A parabolic cover 32 is mounted on the front end of the electro-magnet 25, and co-operates with the shell 26 to provide the proper space dimensions for the exponential function of the horn. The inner end 33, or edge rim, of the parabolic cover 32 meets and fits into a corresponding edge rim 34 of the small end of the horn and the two rim edges are held together by a-split rubber gasket 35 which assures a close t and prevents transfer of undesired vibration.

In order to constitute the horn and the microphone a single megaphone unit, to be available and manipulatable by the operator, I provide a conical bracket 36 to fit down into the space of the conical closure 28 at the back of the horn. u

`The conical bracket 36 supports an annular rubber ring 31 upon which a flange of the shell of the microphone II is seated. A similar annular rubber ring 38 is disposed on the other side of the flange of the microphone shell in such manner that the microphone shell floats between the two rubber rings 31 and 36. A cover, or perforated closure cap 39, presses against the outer rubber ring 31 to hold it in place, and the cover 38 is also provided with a peripheral rim flange that fits over a similar peripheral rim flange 40 on the conical bracket 36 that is in turn secured I5 on the 4back of the megaphone shell in the conical recess 28.

In order to permit the horn to be easily handled and manipulated as a megaphone, a handle 4I is secured to the bottom of the horn shell 26, to serve both as a support for the horn and as a manipulating handle for the horn, to be used by the operator. The trigger switch I4 is disposed in the handle where it can be conveniently operated to closed position by the operator, when it is so desired, and the closure of that switch then connects the A battery to the filament circuit of the two tubes I5 and I6, and to the microphone circuit for the microphone I I.

The microphone Il is adapted to be connected, through the trigger switch I4, and the plug and socket connectors, to the primary winding of the first grid transformer 65. Closure of switch I4 connects the microphone II between ground and one terminal of the primary winding of grid transformer 45.

The microphone control circuit to the first stage tube I5 is provided with a fixed volume control resistor 46 which establishes a limit for the maximum voltage or potential difference available for the control of the first stage amplifier tube I5. The control resistor 46, is connected across the terminals of the secondary of grid transformer. 45.

The voltage drop across the fixed volume control resistor 46 is applied to the grid of tube I5, one end of the resistor being connected to ground.

The output circuit of the first stage amplifying tube I5 is connected through the primary winding of a second audio frequency transformer 41, to the mid point of the B-battery set I8.

The secondary winding of the transformer 41 has each terminal connected to one of th'l grids of the second stage amplifying tube I6, and has its mid point grounded. An output transformer 48 is provided, with each terminal of its primary winding connected to one of the plate electrodes of the second stage amplifying tube I6, and with the mid-point of that primary winding connected to the volt positive terminal of the B-battery.

As shown in the diagram in Figure 3, the filaments of the two amplifying tubes I5 and I6 are connected across the A-battery set I'I.

In addition, the positive terminal of the A-battery set is connected, through a conductor 50, to one terminal of the primary Winding of the input grid transformer 45. The other terminal of that primary winding of transformer 45 is connected to the plug socket terminal 2IC. The corresponding plug terminal 2li-C, in Figure 2, is connected to one terminal or electrode of the microphone II, the other terminal or electrode of the microphone II being connected to a, stationary contact I4-C of the trigger switch I4 on the handle I3 of the megaphone unit.

As already stated, one terminal of the secondary winding of the outputl transformer 48 is connected to the terminal 2 I-D of the main socket 2|. The corresponding terminal 2ll--D of the main plug 20, in Figure 2, is connected to one terminal of the voice coil of the power speaker or reproducer I2. The other terminal of the voice coil of the speaker I2 is connected to the terminal 2li- A of the main plug 20.

The terminal 2I-A on the main socket 2I is connected to ground. And the corresponding terminal 20A of the main plug 20, in addition to being connected to one terminal of the voice coil power speaker I2 is also connected to two movable contacts I4--A on the trigger switch I4.

The contactterminal 2I-B of the main socket 2| is connected to the negative terminal of the A-battery to which is also connected the negative terminal of ythe B-battery. The terminal-B of the main plug connector 2B is connected to a stationary contact terminal I4-C of the trigger switch I6. y

When the system is to be set up for operation, the'main plug 20 at the end of acable 52, extending from the megaphone unit, is plugged into the socket or plug receptacle 2l that is physically mounted and supported on a box (not shown) containing the amplifying equipmentwith the battery sets. This box, containing the amplifying equipment and batteries, is relatively light in weight and may be carried on the person of the megaphone operator and by means of a shoulder strap.

When the operator desires to use the mega-' phone, he closes switch I5, on the handle of the megaphone unit, which thereupon connects the microphone II in series circuit relationship with the primary winding of the grid transformer 45, across the terminals of the A-battery l'l.

This circuit for Ithe microphone, may be traced from the positive terminal of the A-battery set Il, through conductor 50, the primary winding of input transformer 45, the contact terminal 2I-C of the socket 2l, the contact terminal 20-C of the plug 20, the microphone I I, contacts Id--B and I--A of the switch I4, through contact -I-C, plug terminal 2li-B, plug receptacle terminal 2I-B, to the negative terminal of the A-battery set Il.

The above circuit, as closed by the switch I4, thereupon connects the microphone II and the primary winding of the grid transformer 45 across the A-battery.

'Ihe voice coil of the reproducer is permanently connected to the secondary winding of :the output transformer S8, so long as the plug and socket .connection is maintained.

The circuit' of the reproduced voice coil may be traced from the top terminal of the secondary winding of the output transformer 48 to contact 2 I-D of the plug socket 2 I, contact 2U- D of the plug, thence to the voice coil of the reproducer I2, thence to contact 2li-A of the plug, cont'act 2 I-A of the plug socket, and thence to ground at the bottom terminal of the secondary or output winding of the output transformer 48.

Thus the handle switch I4 is employed only to control the connection to the microphone circuit to the A-battery set. i

The provision of an auxiliary microphone unit 55 permits the use of the same megaphone equipment and amplifying equipment by a second operator, who may be distantly located from the rst operator. This arrangement is particularly intended to permit the operation of the main megaphone unit by a drill sergeant on the field, with the auxiliary'microphone available to an inspecting or-supervising officer.

The auxiliary microphone 55, when so employed, is connected through a cable 56 and a trigger control switch 51 to the auxiliary plug 22, which is adapted to fit into the plug receptacle or socket 23, that is physically mounted and supported on the box containing the amplifying equipment and the battery sets.

The auxiliary rmicrophone 55, with its control switch 56, and the connecting plug 22, is connected as shown in the diagram in Figure 4, Closure of the trigger switch 51, connects the auxiliary microphone 55 in the'circuit between yloud commands may be desired.

the A-battery set I'I -and the primary winding of the input grid transformer 45. The auxiliary microphone 55 is thus connected to control the circuit of the input transformer 45, independently of the operation of the main microphone by the main trigger switch I4 on the megaphone unit. This arrangement is made possible by the permanentconnection of the secondary winding of the output transformer 48 to the voice coil of the loud-speaker unit I2 when the main plug and socket connection is established. y

By means of the resistor i6 of fixed resistance in the grid circuit of the rst tube, the maximum potential difference that may be applied to the grid may be pre-determined and limited. By means of this arrangement with a fixed maximum level of amplification, the overall amplification of the system may be kept below the level at which the input system would be responsive to feed back oscillations.

The system may thus be used freely as a megaphone system, by a drill instructor in the field, without being hampered by the development of annoying feed back oscillations that would require constant de-energization of the system during use.

By mounting the carbon microphone I I in such manner as to permit it to fioat between the two annular rubber rings 3l and 38, any mechanical vibration that is set up in the horn body, itself, is absorbed by the rubber gaskets and prevented from affecting the sensitive microphone. y

The microphone is thus safe-guarded against mechanical vibrations directly from the horn, and the amplifying system is safe-guarded against over-amplification, through the sensitive carbon transmitter, by the limiting action of th volume-limit resistor 65.

The megaphone system is thus rendered suitable particularly for eld'use, v/here especially The provision of the auxiliary control, at a remote point from the megaphone, also provides a -desirable feature for a megaphone system of this type, that is to be used on the drill ground.

Mylinvention is not limited to any specific details of construction orv arrangement that are illustrated, since the modifications may be variously made without departing from the spirit and scope of the invention set forth in the appending claims.

I claim as my invention:

1. A power megaphone comprising a loudspeaker unit consisting of an exponential horn and an operating'electro-magnet, the horn being shaped to embody a reflex action return path with the front end of the horn open and the back end of the horn closed with a conical closure; a mounting bracket disposed within the recess of the conical closure on the outside or back side of the horn; a carbon microphone iioatingly supported between two rubber angular washers on said mounting bracket to be free of any mechani- 4 i' 2,314,1oe

2. A power megaphone system comprising an electro-dynamic horn having e. microphone mounted thereon, with a supporting and control handle for manipulating the horn to establish directional control; an external amplifying equipment; a trigger switch on the handle of the horn unit for connecting the horn circuit and the microphone circuit to the external amplifying equipment; a plug and socket connection to provide a circuit connector and disconnector between the horn and microphone as a imit, and the amplifying equipment; and an auxiliary microphone with a plug and socket connector to the amplifying equipment to permit operation of the electro-dynamic horn from a distance, through the auxiliary microphone.

RALPH SILVERMAN. 

